The present disclosure relates to a method for controlling a boat. Moreover, the present disclosure relates to an electronic vessel control unit for steering a boat.
Many types of boats of today are furnished with a propulsion arrangement that includes an engine, such as an internal combustion engine, and one or more drive unit each one of which is equipped with a propeller.
The drive may be attached to the bottom or the stern of the boat. The drive unit may be pivotable around a steering axis such that the direction of travel of the boat may be altered.
For the safety and/or comfort of the occupants of a boat, it is generally desired that the inclinations, e.g. the roll and the trim, of the boat are kept within preferred ranges during the driving of the boat.
The inclinations obtained whilst driving the boat may depend on at least one of the following parameters: the speed of the boat, the steering angle of the boat and the shape of the hull.
As such, a system that is adapted to ensure that inclinations of the boat are within appropriate inclination ranges may generally have to be adjusted to the specific type of the boat, e.g. to specific characteristics of the hull and/or specific characteristics of the propulsion system of the boat. This in turn may result in a cumbersome design procedure and/or manufacturing procedure.
It is desirable to provide a method for dynamically controlling the inclination in at least one direction of a boat.
As such, an aspect of the present disclosure relates to a method for controlling a boat. The boat is adapted to float in a body of water. Moreover, the boat comprises a hull having a longitudinal extension along a hull longitudinal axis, a lateral extension along a hull lateral axis and a vertical extension along a hull vertical axis. The boat also comprises a set of drive units. The set of drive units comprising at least one drive unit. Each drive unit in the set is arranged such that it, during driving of the boat, is:                adapted to be at least partially submerged into the body of water;        adapted to be pivotable, relative to the hull, around a drive unit longitudinal axis that is substantially parallel to the hull longitudinal axis such that a drive unit roll angle can be varied, and        adapted to be pivotable, relative to the hull, around a steering axis that forms an angle with the drive unit longitudinal axis such that a drive unit steering angle can be varied.        
The method comprises:                establishing a boat roll threshold value;        determining a target boat roll angle, and        positioning each drive unit in the set of drive units such that it assumes a drive unit steering angle and a drive unit roll angle such that a resulting boat roll angle is obtained, the absolute value of the difference between the resulting boat roll angle and the target boat roll angle being smaller than the boat roll threshold value.        
Thus, with a control method according to the above, the boat roll angle may be controlled by virtue of the fact that the each drive unit is pivotable around two axes of rotation, viz the drive unit longitudinal axis and the steering axis. This implies that the control method may be used for any boat that has one or more drive units that are adapted to be pivoted around the above two axes of rotation. This in turn implies a reduced need for modifying the hardware of the boat, such as the shape of the hull or the type of propulsion system, in order to obtain appropriate roll characteristics doting operation.
Furthermore, the method according to the above implies that the control method may be adjustable to different driving conditions and/or different environmental conditions.
Optionally, the method further comprises:                establishing a boat direction threshold value;        determining a target boat direction of travel, and        positioning each drive unit in the set of drive units such that it assumes a drive unit steering angle and a drive unit roll angle such that a resulting boat direction of travel is also obtained, the absolute value of the difference between the resulting boat direction of travel and the target boat direction of travel being smaller than a the boat direction threshold value.        
As such, in the above alternative of the control method, the boat roll angle and the boat direction of travel may be controlled simultaneously by pivoting each one of the drive units around the above two axis.
Optionally, the method further comprises:                determining the speed of the boat, and        determining the target roll angle based on the target direction of travel as well as the speed of the boat.        
The fact that the target roll angle is based on the target direction of travel as well as the speed of the boat implies that there is an appropriately low risk that the boat will capsize, even if the boat makes a sharp turn at a high speed.
Optionally, the target roll angle is determined using a roll angle control model that uses input comprising the following parameters: the direction of travel, the speed and selected driving characteristics. Thus, an operator of a boat may be able to select the roll level on the basis of the operator's preferences.
Optionally, the set of drive units comprises at least two drive units. The method further comprises:                establishing a boat trim angle threshold value;        determining a target boat trim angle, and        positioning each drive unit in the set of drive units such that it assumes a drive unit steering angle and a drive unit roll angle such that a resulting trim angle is obtained, the absolute value of the difference between the resulting trim angle and the target boat trim angle being smaller than the boat trim angle threshold value.        
The above alternative of the control method according to the present disclosure implies that the trim of the boat may be controlled even if one or more of the two drive units is mounted to the stem of the boat. This in turn implies increased possibilities to control the behavior of the boat.
Optionally, the boat may comprise a steering actuator. The target boat direction of travel may be determined by determining the position of the steering actuator.
A second aspect of the present disclosure relates to an electronic vessel control unit for steering a boat. The boat is adapted to float in a body of water. The boat comprises a hull having a longitudinal extension along a hull longitudinal axis, a lateral extension along a hull lateral axis and a vertical extension along a hull vertical axis. The boat also comprises a set of drive units. The set of drive units comprises at least one drive unit. Each drive unit in the set is arranged such that it, during driving of the boat, is:                adapted to be at least partially submerged into the body of water;        adapted to be pivotable, relative to the hull, around a drive unit longitudinal axis that is substantially parallel to the hull longitudinal axis such that a drive unit roll angle can be varied, and        adapted to be pivotable, relative to the hull, around a steering axis that forms an angle with the drive unit longitudinal axis such that a drive unit steering angle can be varied.        
The electronic vessel control unit is adapted to:                establish a boat roll threshold value;        determine a target boat roll angle, and        issue a control signal to each drive unit in the set of drive units, the control signal being indicative of a drive unit steering angle and a drive unit roll angle such that a resulting boat roll angle is obtained, the absolute value of the difference between the resulting, boat roll angle and the target boat roll angle being smaller than the boat roll threshold value.        
It should be noted that the appended drawings are not necessarily drawn to scale and that the dimensions of some features of the present invention may have been exaggerated for the sake of clarity.